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  • Insert angles

    I came into a carbide insert today- it's a triangular KC850. It has cutting edges prepared on both sides, which means that it's not tapered for clearance. I'm thinking that the suitable holder might have a slight angle on the seating area to lend this clearance angle to it. Does that make sense? My current holder has the seating area perpendicular to the workpiece, but it uses inserts which are tapered on the three sides. This provides a definite clearance angle.

    Because the corners on this insert also don't taper, I'm thinking that it should also be given a seating surface that puts the 'back' tip of the corner slightly closer in towards center than the leading corner- again to provide some clearance. Does this make sense?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    You are absolutly correct. If you google tng toolholder or tnmg toolholder,you can look at images that show the angle
    Last edited by Edwin Dirnbeck; 03-13-2013, 08:28 PM.

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    • #3
      I have used holders like that.
      They are for roughing(in my case) the seat is slanted in both x and z directions to provide for clearance angles.
      I can not see how your regular holder might work for it. As all the inserts like that i have seen have hook type locking mechanism as opposed to regular torx screw

      Also wall angles on the pocket should match that of your insert, otherwise you will not get proper support and very likely to rip the insert out when machining
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      • #4
        When i made the previous holder, I milled the seat area so the side of the insert could nest against a shoulder, a bit below the cutting edges. With this insert I'll do the same, but I'll also try to provide a bit of clearance for the cutting edges on the back side where it faces the holder. It could be that all I'll need to do is use a diamond point in a dremel to relieve a very little bit of material. But I haven't actually looked at the seat area very well yet- it's possible that the insert top to bottom is slightly wider than the cutting edges.

        I'm well aware that the insert benefits from a most solid clamping arrangement. One tool I made up some time ago uses a steel ball sandwiching the insert between a clamping piece and the body of the holder. The clamping piece allows for a much larger hold-down screw, plus it allowed me to use the insert tucked into place as a locator for the clamp and ball. It works fine, but I lose the tiny ball about every second time I need to rotate the insert. I'll probably look at grinding the end of a larger set screw to fit the insert nicely, then thread that into a clamping piece, using it to again align the clamp so the clamp can be mounted permanently. This holder will be about two inches in diameter, so at least there will be room for some substantial thickness in the clamp as well as the rest of the holder.

        Edwin, thanks for the confirmation of the need for those angles. I will look at some pics to get an idea of how many degrees. I suspect that won't be rocket science-

        And there it is- looks like 7 degrees in two directions, and 3 degrees in the other.
        Last edited by darryl; 03-13-2013, 09:28 PM.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Originally posted by darryl View Post
          I came into a carbide insert today- it's a triangular KC850. It has cutting edges prepared on both sides, which means that it's not tapered for clearance. I'm thinking that the suitable holder might have a slight angle on the seating area to lend this clearance angle to it. Does that make sense? My current holder has the seating area perpendicular to the workpiece, but it uses inserts which are tapered on the three sides. This provides a definite clearance angle.

          Because the corners on this insert also don't taper, I'm thinking that it should also be given a seating surface that puts the 'back' tip of the corner slightly closer in towards center than the leading corner- again to provide some clearance. Does this make sense?
          KC850 is the carbide grade and coating on the insert. It does not tell you the chipbreaker geometry, or what type of cutting the insert is designed for. The insert you have is called "negative", and the toolholders for it tilt the insert downwards as you said.

          The toolholder you currently have is called "positive".

          Edit: KC850 is an older kennametal grade, and is usually associated with roughing inserts. In other words, it probably won't work well for you, so I wouldn't bother making a holder for it.

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          • #6
            What is the full discription of the insert (part #) and what type of lathe. Even though we have established that it is a TNXX series of insert that Fits a TN type holder that does not mean the insert itself is a negative rake insert. Some TN, CN, DN, WN and VN insetrs are formed with a positive rake cutting edge. Plus in the insert number there wil be a group of three numbers. For example a TNMG 432. The last number discribes the radius of the insert tip. The smaller the number the smaller the radius. Small radius are generally finishing inserts. The number of inserts that can fit a TN or other negative rake holders is mind boggling. They vary by radius, carbide component, coatings, chip breaker designs, ceramic, CBN (cubic boron nitride) or diamond tip.

            Now this is my opinion so take it for what it worth*. Most small hobbiest lathes lack the HP and rigidity to take advantage of negative rake inserts with the exception of positive rake finishing inserts. TP, CP and others are a whole different ball game. A 14" machine might or might not be able to. It depends on just how ridgid it is. If the insert has what looks like a lip around its outer edge, no matter how pretty that TiN coating might look, run not walk away as fast as you can. If you do find a N type insert that you can use IMO the WN series is bset as it gives the most bang fro the buck.

            *About what John Nance Garner said about the Vice-Presidency
            Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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            • #7
              I fail to understand the reasoning behind spending hours making a toolholder for a $2 insert that may be good for nothing you do.

              This kind of thing is why one guy gets lucky and says "carbide tools are the greatest thing since sliced bread", while another says "complete waste of money." Somewhere between the two extremes lies reality. I think we all have some cutting tools that we don't use. I certainly do, but I'm not going to spend time adapting them just to try them.

              Without learning more about the technology, why spend so much time making something you can find on Ebay for about $15? The TNMG insert would use one of two basic types of retention for the insert. Traditional, common tool holders use a carbide seat under the insert, an eccentric cam-type screw through the seat pushes the insert back into the pocket and a clamp over the top holds it down. The newer holders use a thicker seat without eccentric, and top clamp that has a pin which fits into the insert hole. As you tighten the clamp down, the back of the clamp slides down an angle and pulls the insert down into the pocket in one motion. This is what one of those looks like:



              Here's one of each style. The MVJNR 163D holder on the left has the eccentric screw and common top clamp. The DDJNR 164D on the right has the new system.



              Your time would be better spent learning about insert geometry, chipbreaker designs, coatings, grades and applications. It's not the most simple thing, but no harder than many others.
              Last edited by PixMan; 03-14-2013, 08:12 AM.

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              • #8
                All that's on this insert is KC850- no other info at all. I asked at a machine shop what inserts they use, and they came out with this one. He said it was kind of a general purpose insert. It does have some positive rake even after you add the clearance angle. I haven't found a picture that matches it yet, but regardless- the advice to learn all about inserts is good.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  KC850 is just the grade. It's a Kennametal insert - the rest of the part number you works out from the size and geometry. Here's a few : http://www.carbidedepot.com/Dynamicl...ategoryID=4287

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                  • #10
                    Thanks for that page, lakeside. Looks like what I have is a tnmp331 kc850.

                    I've just spent the last hour or so reading what I could find about inserts, grades, selection, etc. It would seem that this insert could be useful for light roughing, which to me means getting rid of scale and leveling off an uneven surface. That's pretty much what I asked for when they gave me this insert. Whether my mill has enough power to make it work satisfactorily is another question. I did read in a couple places that the minimum depth of cut is suggested to be the tip radius dimension, and that was in relation to chip-breaking.

                    I was reminded again of HSS inserts, and this led me into the realm of HSS cutting tools in general. I've experienced the differences between the steels, only knowing what one is when it's printed on the shank somewhere. M2 seems a notch up from some bits I have that merely say HSS on them, but then there's T-15. I wasn't aware that you could buy this grade in 'sticks' like I commonly use and have made several holders for. That's going to be an option for me- and then there's the various T-15 inserts, which seem like they might be the best option considering the relatively low HP and licorice-noodle type of machines that I have. It would seem like I could select one of these to give me a pretty good handle on de-scaling and facing without needing lots of power and the best in rigidity.

                    Somehow I also got sidetracked into a Unimat tools site. I'm familiar with the 'revolutionary' shape of the tooling, since I have a Unimat, but of course at the time I wasn't even aware that there was any such thing an an insert, carbide or not. This tooling isn't inserts per se- it's what I'm calling 'stick type', but it seems it is available in the T-15 grade. It's unlikely that what came with my Unimat lathe is this higher grade, but reading this has got me to thinking that a more solid holder might make it useful on the larger lathe, and possibly on the mill.

                    The most reasonable choice to use in my smaller machines certainly looks like it could be T-15 inserts.
                    Last edited by darryl; 03-15-2013, 03:55 AM.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      Update- I know I went against sage advice to spend time making a holder for this insert, but it was in my hand, and I needed a better solution- anyway I made a holder and gave it a try. Works beautifully! The first test was removing scale from some hot rolled bar, which it did seemingly without effort. The fact that it can do this without making my mill chatter with the interrupted cutting is going to make it a valuable addition to my tooling. The holder will need some cosmetic improvement, but I'll get a picture up soon. One benefit of the way this holder is made is that I can machine a different seat in the opposite end of it for a different insert. I'm still going to look into the T-15 grade and try to make a good choice there.

                      Thank you all for your advice.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #12
                        That's super and good for you.

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                        • #13
                          Here's a couple pics- I tried to get a camera angle so you could see the orientation of the seat.



                          Here it's assembled and ready to go.



                          I set the angles at 6 deg instead of 7, just to keep another degree of rake at the cutting edge. If you look horizontally at the bottom of the insert, it has a 3 degree tilt low towards the outside. It was a bit of a brain cramp at first to get the angle vise set up to mill the seating area, but then drilling the relief hole at the top of the insert, the hole for the hold-down screw, and the milling itself was pretty straightforward. The entire seating area of the insert is touching the holder, and there's lots of clearance between the holder and the workpiece.

                          I'm a little concerned about the taper spinning in the spindle bore, so I might make up another block to clamp around the adapter and install a pin. Since I have a few other bits of tooling using these adapters, I'll be able to transfer the pin block to any of them if there's a chance that it might spin in use. The spindle has two slots for the pin to come up into.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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